JP2007035636A - Rotating anode and manufacturing method of cooling body for rotating anode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray rotating anode made of a carbon fiber material for obtaining high thermal conductivity, and also to provide a manufacturing method of a rotating anode cooling body. <P>SOLUTION: The rotating anode of an X-ray tube is made of a carbon fiber material and includes a cooling body coaxially surrounding a rotation axis and formed in rotation symmetry. A base of the cooling body (14) is a preform manufactured by a tailored fiber placement method (TFP) to obtain high thermal conductivity, the cooling body has a hollow cylindrical shape and is formed integrally, the carbon fiber is extended in parallel or nearly parallel with an axis line (16) throughout the entire length, a thermal conductive rate λ with λ≥250W/mK is provided, the carbon fiber is joined by a base material consisting of carbon, and graphite microcrystals of the base material are aligned along the carbon fiber. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes a rotationally symmetrical cooling body having a rotational axis and made of a carbon fiber material in which carbon fibers pass along the rotational axis, and coaxially surrounding the rotational axis, and a focusing ring extending across the rotational axis. In particular, the present invention relates to a rotating anode of an X-ray tube. The present invention also relates to a method of manufacturing a rotationally symmetric cooling body having a high-conductivity carbon fiber extending along an axis of a rotating anode rotatable around a rotating axis.

  A rotating anode with a cooling body of the type mentioned at the outset is known from German patent DE-B-10304936. The cooling body has a cup-like geometry to sufficiently discharge the high temperature generated on the focusing ring or target surface, and the high thermal conductivity carbon fibers that pass through the interior of the cooling body are connected to the lower side of the target. In addition to the cooling pipe through which the coolant flows through the same axis as the axis of rotation, it ends at an obtuse angle.

  A rotating anode is known from U.S. Pat. No. 5,943,389, in which heat conduction is achieved by a carbon composite in which carbon fibers extending parallel to each other are bonded by a carbon substrate. The thermal conductivity of the carbon fiber is in the range of 400 W / mK to 1000 W / mK.

  A molded article containing carbon fiber, a rotating anode composed of a so-called prepreg, is apparent from Japanese Patent Publication JP-A-61-022546. In that case, the fibers can pass in one direction.

  A rotating anode for an X-ray tube is known from German patent DE-B-4012019. The rotating anode has a hollow anode disk, and the coolant is supplied to the anode disk through a hollow shaft.

  It has been proven that fiber composites are effective for heat removal at the rotating anode. This is because the fiber composite material is lighter than a normally used metal body, so that the rotating anode can rotate at a high frequency and / or have a large diameter. However, as actual experience has revealed, such exhaust heat does not sufficiently satisfy the requirements of highly developed X-ray devices, particularly CT devices. This is because the temperature still increases and this requires frequent interruptions in operation. Furthermore, known rotary anodes using carbon composites often have to incorporate an auxiliary cooling tube through which the refrigerant flows, so the disadvantage is that the rotary anode structure is expensive.

  The cooling body according to EP-A-0629593 for brake linings or electronic devices has a carbon fiber preform with a substrate made of carbon material. Carbon fibers extend parallel to each other. To make the preform, the pitch fibers are first wound around the body of the reel to form a cylinder, which is then cut into pieces and subsequently folded flat. The flat preform plate is then carbonized and graphitized.

  The object of the present invention is to obtain a high thermal conductivity, so that the rotating anode cooled by the cooling body can be used without interruption for a longer time than known rotating anodes. It is in improving the cooling body of a rotating anode, and the manufacturing method of a cooling body. It is also an object of the present invention to make the cooling body have a small weight so that the rotating anode can be rotated at a high frequency and / or formed with a large diameter.

Means for Solving the Problems and Effects of the Invention

  In order to solve the above problems, the rotary anode of the type mentioned at the beginning is improved in the present invention as follows. That is, the base of the cooling body is a preform manufactured by the tailored fiber placement method (TFP), the cooling body has a hollow cylindrical shape, is integrally formed, and the carbon fiber is parallel to the axis over the entire length. Alternatively, they are generally parallel, have a thermal conductivity λ of λ ≧ 250 W / m · K, carbon fibers are bonded by a substrate containing carbon, and the graphite microcrystals of the substrate are aligned along the carbon fibers.

  In accordance with the invention, a cooling body is used in which the carbon fibers are arranged over the entire length parallel or generally parallel to the axis of rotation of the anode body and in contact with the focusing ring of the rotating anode, in particular directly in principle. Also, the carbon substrate graphite microcrystals that bind the carbon fibers are aligned along the fibers, thereby obtaining a high thermal conductivity in the range of 250 W / mK or more, especially 600 W / mK or more, especially 600 W / mK to 650 W / mK. It is done. Moreover, since the graphite microcrystal is added to the carbon fiber, this increases the thermal conductivity. Heat is then radiated from the cooling body itself, ie from the opposite end face with respect to the focusing ring. There is no need for an auxiliary cooling path through which the coolant flows.

  The integrally formed cooling body has the shape of a hollow cylinder, and a support ring can pass along its outer and / or inner surface for stabilization. The support ring is pressure-bonded to the cooling body, for example. The support ring is preferably made of a carbon fiber material (CFC).

  Apart from this, the base of the cooling body is a preform manufactured by the tailored fiber placement (TFP) method. For this purpose, in particular endless carbon long fibers or carbon long fibers are sewn to the fabric substrate, in which case the fibers are arranged in a lightning pattern, so that the fibers are aligned parallel to each other except for the curved ends. Prior to heat treatment of the preform thus made, the curved end is cut off. The carbon long fiber is preferably attached to the fabric base so that the curved end portion projects laterally from the tape-shaped fabric base. It is of course possible to subdivide the fabric base into a tape after the carbon long fibers have been deposited, and simultaneously produce a plurality of bases by the TFP method and then wrap them around a cylindrical body to produce a cooling body.

Accordingly, the present invention provides the following procedure for a rotationally symmetric cooling body of a rotating anode rotatable about a rotation axis, having a high thermal conductivity carbon fiber extending along the rotation axis: In order to fabricate a tape-like preform by the tailored fiber placement method (TFP), the carbon fibers are sewn to the fabric base so that the carbon fibers are parallel or generally parallel to each other.
-Winding the tape-shaped preform around a cylindrical body,
Impregnating the preform with carbon or with a material that converts to carbon by carbonization;
-Heat treating the impregnated preform;
-Re-densify the heat-treated preform once or several times,
-High temperature treatment,
-Also characterized by a manufacturing method by performing mechanical final machining of the cooling body thus produced in order to obtain the final geometric shape of the cooling body.

  In that case, the heat treatment and re-densification are performed by impregnation and heat treatment so that the graphite microcrystals of the substrate binding the carbon fibers are aligned along the carbon fibers. This further increases the thermal conductivity, so that a desired cooling effect can be obtained.

  Based on the fact that the graphite microcrystalline layer is aligned in the carbon fiber and oriented along the fiber surface, select the appropriate processing parameters and the appropriate carbon substrate system along the fiber surface of the substrate graphite crystal. A short-range order is possible. Suitable carbon substrate systems are materials that are well graphitized, such as pitch or pyrographite. Thermally crosslinked resins are not very good in graphitization and should be avoided.

  Graphitization can also be performed in vacuum to align the microcrystals along the carbon fibers. In that case, however, carbon sublimation must be avoided sufficiently. As an alternative or in addition, tension or tension may be applied to the carbon fibers during graphitization. This all results in crystallite alignment along the carbon fibers, resulting in the desired increase in thermal conductivity.

  In order to obtain high thermal conductivity, the volume content of carbon fiber is preferably 40% to 80%, particularly 60% to 70%. This is obtained by winding a preform produced by the tailored fiber placement method around a cylindrical body with a predetermined tension. Preferred tensions include values of 3 kp to 15 kp, especially 5 kp to 10 kp.

  Another way to adjust the volume content of the carbon fibers to the desired value, in particular 60% to 70% by volume, is to use a pressure roller and the roller densifies the fiber sheet when it is wound around the core. .

  The tailored fiber placement method itself is described, for example, in the literature “Mattheij et al: Tailored fiber-placement-mechnical properties and applications”, Journal of Reinforced Plastics and Compsites, Vol. 9 (1998), pages 774-786. To that extent, the disclosure relating to this is clearly cited.

  Since the preform thus prepared usually has a thermal conductivity of 115 W / mK to 200 W / mK in the initial state, this preform is easy to handle for manufacturing a cooling body and has the advantage of having sufficient mechanical properties. Given. As the fibers, graphitizable fibers, or already graphitized fibers, in particular pitch-based carbon fibers, can be used. The diameter of the fiber is preferably in the range 4 μm to 9 μm, in particular 8 μm.

  After winding the preform around the core, heat treatment is performed so that the thermal conductivity is increased in situ. In particular, a thermal conductivity in the range of 600 W / mK to 650 W / mK is preferable. Regardless of this, the thermal conductivity should always be 250 W / mK or higher.

  High thermal conductivity is obtained by stabilizing and fixing the preform fibers by CVI [chemical vapor infiltration] impregnation with pyrolytic carbon or by impregnation with a well graphitized substrate precursor. The preform thus fixed is then subjected to high-temperature heat treatment at a temperature T of T> 2800 ° C. to graphitize both the fiber and the substrate. By fixing the fiber to the substrate, the effect of stretch graphitization due to plastic deformation of the fiber is increased. It is used to increase the thermal conductivity by improving the conversion.

  Prior to dry or wet impregnation, the preform fibers or the preform itself can be treated with resin or pitch and subsequently cured. Next, wet impregnation with resin or pitch or vapor phase impregnation with pyrolytic carbon (PyC) is performed by CVI method. Subsequently, heat treatment is carried out, first carbonization and subsequent graphitization are carried out using resin and pitch, and graphitization is carried out exclusively by dry impregnation. Carbonization to convert the impregnating agent into carbon is carried out especially in the temperature range of 700 ° C. to 1200 ° C., in particular in the range of 900 ° C. to 1050 ° C. The preferred graphitization temperature is in the range of 2400 ° C to 3500 ° C, especially 2600 ° C to 3300 ° C.

  For wet impregnation, high carbon yield materials are used to allow conversion to carbon. In wet impregnation, a heat treatment step precedes carbonization, whereby the impregnating agent is cured or crosslinked, or in the case of pitch, the impregnating agent is melted.

  In order to ensure that undesired shape changes are avoided during the heat treatment, a hollow cylindrical unitary or integral cooling body may be supported on the plate during the heat treatment, in particular surrounded by a support ring.

  In particular, when impregnation is performed after winding the preform on a cylindrical body, it is possible to perform at least partial impregnation immediately.

  After heat treatment, that is, carbonization and graphitization, re-densification is performed to improve thermal conductivity. This includes vacuum-pressure impregnation and curing, carbonization, graphitization. In that case, re-densification can be carried out in particular 2 to 4 times. However, the present invention is not limited thereby.

Re-densification not only improves the thermal conductivity, but at the same time increases the density and minimizes the porosity, so on the other hand the mechanical strength of the cooling body is improved. In particular, re-densification means that the finished cooling body has a continuous porosity of less than 14% by volume, in particular less than 10% by volume, and a density in the range of 1.5 g / cm ³ to 2.2 g / cm ³ , in particular 1.75 g / cm ^3. To 2.0 g / cm ₃ .

  After one or several re-densifications, a high temperature treatment is performed, which can also be called final graphitization. The high temperature treatment is performed in the range of 2400 ° C to 3000 ° C. The cooling body thus manufactured is subsequently processed into a final shape by cutting. In some cases, a high strength support structure in the form of a carbon fiber material ring is attached. The support ring is attached to the inner peripheral surface and / or the outer peripheral surface.

  In order to avoid “particle release”, a CVD (chemical vapor deposition) coating can be applied to the cooling body after final processing, depending on the choice. The coating alone preferably has a high release coefficient of 0.5 ≦ ε <1.0, in particular 0.8 ≦ ε ≦ 0.9.

  It is also possible to clean the cooling body in a high temperature process before coating in this regard. Microcrystal formation is favorably affected by cleaning. This is because particularly fine crystallites are formed at a site where foreign atoms existed before high temperature cleaning. If impurities are removed again during the high temperature cleaning process, they can be used deliberately to improve graphitization and improve thermal conductivity.

  Other details, advantages and features of the present invention are not only from the claims and the features found in the claims-alone and / or in combination-but also from the following description of the preferred embodiments found in the drawings. it is obvious.

  The invention will be described on the basis of a cooling body for the rotating anode 10. However, the present invention is not limited thereby.

  FIG. 1 shows a very schematic view of a rotating anode 10 especially for a computer tomograph. The rotary anode 10 comprises a focusing ring 12 and a cooling body 14 made of tungsten in particular. The rotating anode 10 is supported on a shaft (not shown) and can rotate around the axis 6. In order to obtain a high measurement point density in a short time, the rotating anode is rotated at a frequency of 150 Hz. The diameter ranges from 150 mm to 250 mm. However, this should not be interpreted as a limitation.

  In order to ensure that heat can be well discharged from the focusing ring 12 and thereby the rotating anode can be used without interruption for long periods of time, the cooling body 14 is parallel to the axis 16 and parallel to each other and is A carbon composite composed of bonded carbon fibers. Further, when the cooling body 14 is manufactured, the thermal conductivity is increased in-situ so that the carbon fiber has a thermal conductivity in the range of 250 W / mK or more, particularly 600 W / mK to 650 W / mK. This ensures that the heat discharged from the focusing ring 12 through the cooling body 14 is radiated sufficiently from the end face 18 of the cooling body 14 on the opposite side of the focusing ring.

  The cooling body 14 is made of a preform wound in a spiral shape. The preform is manufactured by the tailored fiber placement method. For this purpose, endless carbon fibers 22 are arranged in a lightning pattern on a fabric substrate 20 having a high carbon yield and sewn. The curved portion 24 is then cut, notably along the edge of the substrate 20, thus resulting in a tape-like preform in which the carbon fibers 22 are aligned parallel to each other and perpendicular to the longitudinal axis of the substrate 12. The preform is then wrapped around a cylinder called the heart, with the carbon fibers 22 being parallel to the axis of the heart. The winding around the core is performed so that a desired fiber volume content is obtained. The fiber volume content is preferably in the range from 40% to 80% by volume, in particular from 60% to 70% by volume. For this purpose, a tension F of 5 kp to 10 kp is applied. As an alternative or in addition, a pressure roller can be used for the preform during winding onto the core. Thereby also the adjustment of the fiber volume content to the desired value takes place or is facilitated. Subsequently, wet or vapor phase impregnation is performed. Wet impregnation is performed with materials having a high carbon yield to allow conversion to carbon. In particular, resin and pitch are mentioned. As the vapor phase impregnation, a CVI method using pyrolytic carbon can be considered.

  It should be mentioned that the fibers can already be treated with resin or pitch before the preform is wound onto the core without departing from the invention.

Regardless of this, the impregnation is followed by a heat treatment and if a resin or pitch is used, the impregnating agent is first cured or crosslinked, while the pitch must be heated to melt before impregnation. The heat treatment includes carbonization and graphitization when using a resin and pitch, and graphitization exclusively in a gas phase impregnation. Carbonization is preferably carried out in the temperature range of 700 ° C. to 1200 ° C., in particular in the range of 900 ° C. to 1050 ° C., whereas graphitization is preferably carried out in the range of 2400 ° C. to 3500 ° C., in particular 2600 ° C. to 3300 ° C. . The heat treatment is followed by cooling, followed by one or several re-densifications. In that case, re-densification includes vacuum-pressure impregnation to increase density and minimize porosity. This increases the mechanical strength of the manufactured cooling body. In particular, it is preferable to re-densify the cooling body 14 so that the density ρ becomes ρ> 1.85 g / cm ³ .

In order to remove impurities, it is preferable to perform gas cleaning.

A filler having high thermal conductivity can be added to the impregnating agent during re-densification.

Alternatively, re-densification, ie impregnation, hardening or graphitization, can be achieved when the cooling body produced has a continuous porosity of 14% or less, in particular 10% or less and / or 1.5 g / cm ³ to 2.2 g / range cm ^3, in particular to 1.75 g / cm ³ not done so as to have a density in the range of 2.0 g / cm ^3.

Next, high temperature treatment is performed in the range of 2400 ° C. to 3500 ° C. Subsequently, the cooling body is processed into a final shape by cutting. In some cases, the cooling body can be provided with a support structure in the form of a high strength carbon fiber material ring. The ring can be attached to the outside and / or the inside of the hollow cylinder.

  Finally, in order to avoid “particle emission”, chemical vapor deposition coatings, for example pyrolytic carbon coatings, can optionally be performed. The coating preferably has a high emission coefficient ε of 0.5 ≦ ε <1, in particular 0.8 ≦ ε ≦ 0.9.

  If cleaning is scheduled, this is preferably done between final processing and chemical vapor deposition coating. Perform hot gas cleaning to improve purity and graphitization. In order to reduce particle emission, ultrasonic cleaning is especially chosen.

  Finally, one support ring 26, 28 made of high-strength carbon fiber material can be crimped to the inside and the outside of the cooling body 14, respectively.

  The preform can be removed from the core prior to each impregnation or heat treatment step. It is of course possible to pull out the preform from the heart after the heat treatment has ended. However, the drawing of the preform should only take place if it is guaranteed at the processing stage to be carried out that the deformation of the preform which is no longer on the heart is prevented. Thus, the preform should surround the heart at least before each high temperature processing stage, even if drawing can be done in the preceding processing stage.

A sectional view of a rotating anode is shown. The preform fragment to be produced is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Rotating anode 12 Focusing ring 14 Cooling body 16 Rotating shaft 18 End surface 20 Fabric base 22 Endless carbon fiber 24 Curved portion 26 Support ring 28 Support ring

Claims (22)

  A rotationally symmetric cooling body (14) having a rotational axis (16) and made of a carbon fiber material in which carbon fibers pass along the rotational axis (16), and coaxially surrounding the rotational axis; With a focusing ring (12) extending across, especially in the rotating anode (10) of an X-ray tube, the base of the cooling body (14) is a preform manufactured by the tailored fiber placement (TFP) method. The cooling body has a hollow cylindrical shape, is integrally formed, and the carbon fiber (22) is parallel or substantially parallel to the rotation axis (16) over the entire length, and the thermal conductivity λ ≧ 250 W / mK. A rotating anode, wherein carbon fibers are bonded by a substrate containing carbon, and graphite fine crystals of the substrate are aligned along the carbon fibers.   2. Cooling body according to claim 1, characterized in that the cooling body (14) has a support ring (26, 28) along its outer or inner surface.   3. Cooling body according to claim 2, characterized in that the support ring (26, 28) is crimped onto the cooling body.   The cooling body according to claim 2 or 3, wherein the support ring (26, 28) is made of a carbon fiber material (CFC). The cooling body (14) has a density ρ of 1.5 g / cm ³ ≦ ρ ≦ 2.2 g / cm ³ , in particular 1.75 g / cm ³ ≦ ρ ≦ 2.0 g / cm ^3. The cooling body according to 1. In a method of manufacturing a rotationally symmetric cooling body having a high thermal conductivity carbon fiber (22) extending along the axis of a rotating anode (10) rotatable about the axis of rotation, the following procedure is used: The carbon fiber (22) is sewn to the fabric substrate (20) so that the carbon fibers are parallel to each other or generally parallel to each other in the preform, and the tape-like preform is formed by the tailored fiber placement method (TFP). Make a renovation,
-Winding the tape-shaped preform around a cylindrical body,
Impregnating the preform with a material that is converted by carbon or by carbonizing carbon;
-Heat treating the impregnated preform;
-Re-densify the heat-treated preform once or several times,
-High temperature treatment,
A method characterized in that a mechanical final machining of the cooling body thus produced is carried out in order to obtain the final geometric shape of the cooling body.   Carbon fibers (22) in the form of long carbon fibers or endless carbon fibers are sewn onto the fabric substrate (20) in a lightning pattern, and in particular, the curved portion (24) protruding from the edge of the fabric substrate is cylindrical. 7. A method according to claim 6, characterized in that it is cut off before being wound on the body or after the preform has been removed from the cylindrical body.   7. The method according to claim 6, wherein the preform is treated with a resin or pitch before or after winding.   The preform is wound around the cylindrical body with a tension F so that the fiber volume content V of the wound preform is 40% by volume ≦ V ≦ 80% by volume, in particular 60% by volume ≦ V ≦ 70% by volume. The method according to claim 6.   10. Method according to claim 9, characterized in that the tension F is adjusted to 3 kp ≦ F ≦ 15 kp, in particular 5 kp ≦ F ≦ 10 kp.   The method according to claim 6, wherein a pressure roller acts on the preform when winding on the cylindrical body.   The method according to claim 6, wherein the preform wound around the cylindrical body is impregnated by vapor phase impregnation or liquid impregnation.   The method according to claim 12, wherein vapor phase impregnation is performed with pyrolytic carbon (PyC). 9. The preform is carbonized at a temperature T _C of 700 ° C. ≦ T _C ≦ 1200 ° C., particularly 900 ° C. ≦ T _C ≦ 1050 ° C., when the preform is treated with a resin or pitch. the method of. 15. The process according to claim 6 or 14, characterized in that the impregnated preform is graphitized at a temperature T _G of 2400 ° C. ≦ T _G ≦ 3500 ° C., in particular 2600 ° C. ≦ T _G ≦ 3300 ° C.   The method according to claim 6, wherein the material used for impregnation comprises a highly thermally conductive filler.   7. The cooling body according to claim 6, characterized in that after the final machining of the cooling body, the cooling body is coated with a material having an emission coefficient ε of 0.5 ≦ ε <1, in particular 0.8 ≦ ε ≦ 0.9. Method. The method of claim 17, wherein coating the cooling body by CVD pyrolytic carbon by (chemical vapor deposition) method (P _y C).   7. A method according to claim 6, characterized in that after the final processing and before the coating, the cooling body is subjected in particular to gas cleaning or ultrasonically cleaned.   The method of claim 6, wherein the preform is withdrawn from the cylinder after the high temperature treatment.   7. The method of claim 6, wherein the preform is impregnated with a well graphitized material, such as pitch or pyrolytic carbon, to align the graphite crystallites along the carbon fibers. 7. Process according to claim 6, characterized in that carbon fibers having a diameter D of 4 [mu] m≤D≤9 [mu] m are used for the production of preforms.

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